Synergistic effects of melatonin and dienogest on pain relief in endometriosis: a randomized controlled trial

Objective Endometriosis affects 5-10% of reproductive-aged women and is characterized by chronic pelvic pain, dysmenorrhea, dyspareunia, and infertility. Standard hormonal therapies, such as dienogest, effectively manage symptoms , but are often associated with side e ffects and high recurrence rates after discontinuation. This study investigated the efficacy of melatonin as an adjunct to dienogest for reducing endometriosis-associated pain.

Ninety-four women with ultrasonography -confirmed ovarian endometrioma were randomized 1:1 to receive melatonin+dienogest or placebo+dienogest for 6 months. Analyses were performed on both per-protocol (PP ; n=52) and intention -to-treat bases (ITT ; n=94). The primary outcome was dysmenorrhea measured using the visual analog scale. The secondary outcomes included dyspareunia, pelvic pain, dyschezia, quality of life (World Health Organization quality of life-brief version [WHOQOL- BREF]), and clinical symptoms (Biberoglu&Behrman [B&B] scale).

Dysmenorrhea scores decreased significantly more in the melatonin arm (Δ= -1.3 points; P=0.011 PP; Δ=-1.2; P=0.014 ITT). No significant between -group differences were observed in dyspareunia, pelvic pain, or dyschezia. WHOQOL -BREF scores improved by 6.5±9.2 points in the melatonin group and 5.9±8.7 in the placebo group ( P=0.71). B&B composite pain scores decreased by 4.1±2.9 (melatonin) and 3.8±3.0 (placebo) (P=0.64). No serious adverse events occurred; however, vertigo was more frequent in the melatonin group (53.8% vs. 7.7%).

Adjunctive melatonin therapy with dienogest significantly improved dysmenorrhea compared with dienogest alone. However, the addition of melatonin did not yield significant improvements in other pain domains or quality of life indices. These results support the use of melatonin as a targeted adjunct treatment for menstrual pain during endometriosis.

Endometriosis; Melatonin; Dienogest; Dysmenorrhea; Pain management

Endometriosis is a chronic gynecological condition characterized by the presence of endometrium -like tissue outside the uterus, affecting approximately 5-10% of women globally [1-3]. The condition typically presents with dysmenorrhea, dyspareunia, and infertility, with lesion phenotype s contributing variably to disease severity [1-4]. From menarche to menopause, endometriosis significantly impairs quality of life by disrupting personal relationships, social activities, and productivity, thereby imposing a substantial socioeconomic burden [2,3,5,6]. Its pathophysiology involves chronic inflammation mediated by proinflammatory cytokines and altered immune responses. This often requires multiple surgical interventions and is associated with psychiatric comorbidities, obstetric complications, and other chronic diseases [1,3-7]. The standard management in cludes analgesia, hormonal therapy, and surge ry. Progestins, particularly dienogest, are the cornerstone of medical management. Dienogest suppresses ectopic endometrial growth and alleviates pain by inducing anovulation and creating a hypoestrogenic environment that inhibits inflammation and promotes apoptosis in endometrial cells [3,8]. Despite their efficacy, hormonal therapies are limited by side effects , such as weight gain and mood instability, as well as high symptom recurrence rates upon cessation. Furthermore, approximately one-third of women exhibit progesterone resistance, necessitating complex treatment adjustments [3,4,6,9]. Melatonin, an indolamine primarily synthesized in the pineal gland, has been proposed as a potential adjunctive therapy for endometriosis because of its anti -inflammatory and antioxidant properties. Interest in non -hormonal and adjunctive strategies has increased in response to the substantial symptom burden, impaired quality of life, and limitations associated with standard medical treatments for endometriosis, including side effects, reduced tolerability, and recurrence after treatment discontinuation [1,4-6,9]. However, clinical data evaluating the efficacy of melatonin in combination with established hormonal therapies, such as dienogest, remain limited. This study aimed to evaluate the effectiveness of melatonin combined with dienogest at reducing pain severity (visual analog scale [VAS]) and improving quality of life and sexual function (World Health Organization quality of life-brief version [WHOQOL-BREF] and Biberoglu&Behrman [B&B] scale) over a 6-month treatment period [10,11].

1. Study design and participants This randomized, double-blind, placebo-controlled clinical trial assessed the efficacy of melatonin as an adjunct to dienogest for the treatment of endometriosis-associated pain. The study was conducted at an academic hospital from January 2023 to January 2024. The study protocol was approved by our Institutional Ethics Committee. Written informed consent was obtained from all participants. Eligible participants were reproductive-age women (20-50 years) with a transvaginal-ultrasound- confirmed diagnosis of ovarian endometrioma (>2 cm) and moderate -to-severe endometriosis-related pain (VAS score ≥4 for dysmenorrhea, dyspareunia, or chronic pelvic pain). Exclusion criteria included a history of malignancy, cardiovascular disease, deep infiltrating endometriosis (DIE), hormonal treatment within the previous 3 months, or contraindications to dienogest or melatonin. 2. Randomization and blinding Ninety-four participants were randomized in a 1:1 ratio to the melatonin or placebo arm using block randomization (block size of six) via SealedEnvelope.com. The allocation was concealed using sequentially numbered opaque packages. The participants, care providers, and outcome assessors were blinded. 3. Intervention protocol Participants in the intervention group received 2 mg of dienogest daily and 10 mg of melatonin once nightly (1 hour before bedtime). The control group received 2 mg of dienogest daily and a nightly matched placebo dose. The treatment duration was 6 months. Melatonin and matching placebo tablets were sourced from Jalinus Pharmaceutical Company (Tehran, Iran), whereas dienogest was supplied by Aburaihan Pharmaceutical Company (Tehran, Iran). 4. Outcome measures The primary outcome was a reduction in dysmenorrhea severity assessed using the VAS. Secondary outcomes included pelvic pain, dyspareunia, dyschezia, quality-of-life (WHOQOL-BREF) [11], and clinical symptoms (B&B scale) [10]. Outcomes were measured at baseline and after 6 months. Safety was assessed using monthly adverse event screening. 5. Follow-up and adherence The participants attended monthly on-site visits for adverse event screening, vital sign monitoring, and medication adherence verification via pill counts. The final 6-month visit included a repeat transvaginal ultrasound and VAS pain assessment. To reinforce adherence, participants received reminders via telephone or messaging apps 48 hours prior to visits and 7 days post-dispensing. "Study completion" was defined as attendance at the final 6-month in-person visit. Telephone contact alone was insufficient. Participants were classified as lost to follow-up after three unsuccessful contact attempts. 6. Statistical analysis The sample size was calculated using NCSS PASS ver 15 (COMPANY, CITY, STATE, COUNTRY), assuming a type I error of 5%, 80% power, and a 1 -point difference in the VAS, requiring 47 participants per group (allowing for 20% attrition). Efficacy was analyzed in both the intention-to-treat (ITT) population (n=94) using mixed-effects models with multiple imputations for missing data and the per-protocol (PP) population (n=52). Between-group differences were assessed using independent Student’s t-tests and chi-square or Fisher exact tests for categorical variables. Data analysis was performed using Stata version 16 (StataCorp, College Station, TX, USA), with significance set at P<0.05.

Of the 94 randomized participants, 52 (55.3%) completed the 6-month protocol (26 per arm). The reasons for attrition are detailed in Fig. 1. The baseline demographic and clinical characteristics, including endometrioma laterality and cyst size, were well balanced between the groups (Table 1). 1. Primary outcome: dysmenorrhea In the PP analysis, dysmenorrhea scores decreased significantly in both groups; however, the reduction was significantly greater in the melatonin group than the placebo group (mean difference [MD], -1.3; 95% confidence interval , 0.3-2.3; P=0.011) (Table 2). ITT analysis confirmed these findings (MD, 1.2; P=0.014) (Table 3). 2. Secondary pain outcomes Both groups exhibited improvements in dyspareunia, pelvic pain, and dyschezia from baseline. However, there were no statistically significant differences in the magnitude of the reduction between the melatonin and placebo groups at 6 months (Table 4). Dysuria scores were negligible in both groups. 3. Quality of life and clinical symptoms Both groups showed improvements in WHOQOL-BREF scores (melatonin, 6.5±9.2 vs. placebo, 5.9±8.7; P=0.71) and reductions in B&B composite scores ( melatonin, -4.1±2.9 vs. placebo, -3.8±3.0; P=0.64). No significant inter-group differences were observed (Table 4). 4. Adverse events Vertigo was significantly more frequent in the melatonin group (53.8%) than in the placebo group (7.7%) (P=0.001). The incidence of spotting was high in both arms (melatonin, 50.0% vs. placebo, 57.7%), but did not differ significantly between arms (P=0.58). No serious adverse events were observed (Table 5).

This trial demonstrated that adding melatonin to dienogest therapy resulted in a statistically significant improvement in dysmenorrhea compared with dienogest therapy alone. However, we observed no significant additional benefits for non-menstrual pelvic pain, dyspareun ia, or dyschezia. Quality of life and composite pain indices (B&B, WHOQOL-BREF) improved modestly in both arms, without evidence of the superiority of the melatonin adjunct. These findings suggest that the analgesic effects of melatonin on endometriosis may be mechanism -specific, rather than universally applicable to all pain domains. The biological plausibility of using melatonin as an adjunct stems from its anti -inflammatory, antioxidant, and immunomodulatory properties [12,13]. Melatonin reduces oxidative stress and inhibits estrogen-driven pathways, which are mechanisms that complement the established progestogenic effects of dienogest [14]. By targeting these overlapping molecular pathways, combination therapy can enhance pain management and suppress endometriotic cell proliferation. Our findings regarding dysmenorrhea are consistent with preclinical data showing that melatonin reduces endometrial lesion volume and oxidative stress markers in animal models [15,16]. However, the clinical data are mixed. While some studies have suggested that melatonin reduces chronic pelvic pain [17], others, such as that by Söderman et al. [18], found no benefit over placebo in terms of pain reduction. Our results support the hypothesis that melatonin acts synergistically with hormonal treatments, speci fically for menstrual pain, potentially by amplifying the anovulatory and anti - inflammatory environment created by dienogest. The heterogeneous responses observed across the pain domains were notable. Dysmenorrhea is driven predominantly by prostaglandin -E2-mediated inflammation and oxidative stress. Melatonin attenuates these pathways by scavenging reactive oxygen species and downregulating COX-2 synthesis [14,19]. Additionally, melatonin exerts direct analgesic effects by activating the MT2 and opioid receptors, as demonstrated in preclinical pain models [20]. In contrast, dyspareunia is often multifactorial, involving DIE, fibrosis, pelvic floor hypertonicity, and structural generators that may respond less to pharmacological anti -inflammatory therapy alone [1,3]. This mechanistic divergence, along with potential dosing limitations for fibrotic lesions, may explain the lack of significant improvement in dyspareunia scores in our trial. 1. Limitations This study ha s several limitations. First, the attrition rate was higher than anticipated (44.7%), likely because of the strict monthly follow-up protocol, although ITT analyses confirmed the primary findings. Second, the 6-month study duration captured only early analgesic effects. A longer follow-up is required to assess durability and disease progression, as endometriosis is a chronic and frequently recurrent condition, despite medical and surgical management [21]. Third, eligibility was restricted to patients with ultrasonography -confirmed ovarian endometrioma; therefore, patients with isolated peritoneal disease or DIE were not specifically represented. Finally, we used a fixed 10 mg nightly dose of melatonin. Future dose -ranging studies are needed to balance efficacy with tolerability, particularly given the significantly higher incidence of vertigo (53.8%) in the trea tment arm. Beyond these limitations, complementary and integrative approaches may offer additional benefits for symptom control in women with symptomatic endometriosis [22]. Combining melatonin with dienogest significantly enhanced the relief from dysmenorrhea in women with endometriosis-associated pain compared to dienogest alone. Although it did not provide superior relief from dyspareunia or non-menstrual pelvic pain in this cohort, this combination offers a targeted option for patients with refractory menstrual pain. Conflict of interest The authors declare no potential conflicts of interest. Ethical approval The study was registered and approved by the Ethics Committee of Tehran University of Medical Sciences as a clinical trial under the code IR.TUMS.IKHC.REC.1401.224. Patient consent Funding information This study did not receive any financial support.

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Baseline demographic and clinical characteristics of the study participants Variable Placebo (n=26) Melatonin (n=26) P-value Age (yr) 37.1±7.6 39.0±4.8 0.273 BMI (kg/m²) 24.6±4.9 26.1±3.8 0.236 Gravidity 1.3±1.2 1.6±1.3 0.296 Parity 1.1±1.0 1.2±1.0 0.588 Waist circumference (cm) 85.0±12.8 88.9±11.3 0.258 Education 0.266 Diploma 12 (46.2) 14 (53.8) Smoking status 0.691 Current smoker 13 (50.0) 16 (61.5) Non-smoker/former 13 (50.0) 10 (38.4) Endometrioma characteristics Laterality (right/left/bilateral) 12/9/5 11/10/5 0.96 Mean cyst diameter (cm) 4.2±1.3 4.0±1.4 0.57 Multiple cysts (>1) 7 (27.0) 8 (31.0) 0.76 Values are presented as mean±standard deviation or number (%). There were no statistically significant differences between the groups at baseline. BMI, body mass index. Table 2. Visual analog scale pain scores at baseline and 6-month follow-up assessments (per-protocol analysis) Symptom Baseline 6 months Change (Δ)a P-valueb Dysmenorrhea Placebo 7.0±2.5 4.3±1.9 -2.7±1.4 0.011 Melatonin 6.5±2.2 2.5±1.5 -4.0±2.1 Dyspareunia Placebo 4.0±3.1 2.6±2.2 -1.4±1.3 0.078 Melatonin 4.1±2.8 1.7±1.8 -2.3±2.2 Pelvic pain Placebo 5.0±2.6 3.2±2.2 -1.8±1.1 0.077 Melatonin 4.6±3.3 1.6±1.7 -2.9±2.9 Dyschezia Placebo 2.9±2.8 1.4±1.9 -1.5±1.5 0.620 Melatonin 1.7±2.2 0.4±0.7 -1.3±1.7 Dysuria Placebo 0.2±0.4 0.0±0.2 -0.1±0.4 0.480 Melatonin 0.2±0.6 0.0±0.0 -0.2±0.6 Values are presented as mean±standard deviation or number (%). aChange (Δ) was calculated as (6-month score-baseline score). bP-values represent the comparisons of the change scores (Δ) between the placebo and melatonin groups using an independent Student’s t-test. Table 3. Intention-to-treat analysis of pain score reductions (n=94) Symptom Placebo (Δ) Melatonin (Δ) P-valuea Dysmenorrhea -2.6±1.5 -3.8±2.0 0.014 Dyspareunia -1.3±1.4 -2.2±2.0 0.090 Pelvic pain -1.7±1.2 -2.8±2.5 0.080 Dyschezia -1.4±1.6 -1.2±1.5 0.670 Values are presented as mean±standard deviation. aMixed-effects linear regression models with multiple imputations for missing data. Table 4. Secondary outcomes: quality of life and clinical symptoms (change from baseline) Outcome measure Placebo (n=26) Δ Melatonin (n=26) Δ P-value WHOQOL-BREFa 5.9±8.7 6.5±9.2 0.71 B&B scaleb -3.8±3.0 -4.1±2.9 0.64 Values are presented as mean±standard deviation. WHOQOL-BREF, World Health Organization quality of life; B&B, Biberoglu&Behrman. aWHOQOL-BREF: brief version (higher scores indicate improvement). bB&B scale: lower scores indicate improvement. Table 5. Incidence of adverse events during the 6-month treatment period Adverse event Placebo (n=26) Melatonin (n=26) P-value Vertigo 2 (7.7) 14 (53.8) 0.001a Spotting 15 (57.7) 13 (50.0) 0.578b Serious adverse events 0 (0.0) 0 (0.0) Values are presented as number (%). aFisher’s exact test. bChi-square test.